As is generally known in the art, reinforced concrete pipes are classified by the manufacturing method into centrifugal reinforced concrete pipes and vibrated and rolled (VR) reinforced concrete pipes. The reinforced concrete pipes are produced from a no-slump concrete mixture by a vibrating and compressing method, and are used as drainage pipes, water supply pipes, agricultural water pipes, industrial water pipes, and so on.
As shown in FIG. 1, in the reinforced concrete pipes, the gap of a joint or a seam connected in a collar type or a socket type is filled with a filler such as composition mortar. However, the filler falls out of the gap, and thus it is difficult to keep the joint watertight. For this reason, a rubber ring 4 is used as a primary joining material for joining connector parts 1 and 2 of the watertight reinforced concrete pipes that have recently been developed, and composition mortar as a secondary joining material is injected between the connector parts, so that the pipes withstand high hydraulic pressure. However, differential settlement of a pipe line occurs due to compaction of the ground, insufficient foundation work, or careless construction practices.
Meanwhile, to prevent a tremendous concentrated load P such as that from soil pressure above the pipe, the load of vehicles, and a dead load of the pipe from being directly applied to the rubber ring 4 between the pipes, another method of simultaneously injecting the rubber ring 4 and the composition mortar as the secondary joining material is used, so that the rubber ring 4 is responsible for handling only the hydraulic pressure, while the composition mortar takes charge of the concentrated load P. However, due to either the breakdown of the injected composition mortar for failing to withstand the concentrated load P or the differential settlement, it is impossible to accomplish the desired purpose of external water flowing into the pipes or internal water flowing out of the pipes. Particularly, a large quantity of external water, i.e. infiltration or inflow, is generated. Recently, pipe maintenance work has been carried out on a large scale for the purpose of protecting the environment and improving the quality of water.
To solve this problem, many inventions have been proposed, representative examples of which are Korean Utility Model Registration No. 333394, entitled “THE CONNECTING STRUCTURE OF THE CONCRETE PIPES” (hereinafter, referred to as “Cited Invention 1”) and Korean Patent No. 726736, entitled “FIXING CONSTRUCTURE OF DRAINAGE” (hereinafter, referred to as “Cited Invention 2”). As for the construction of each invention, Cited Invention 1 is constructed, as in shown in FIG. 2, so that cross section L-shaped circular angles 3 and 3′ are inserted into a spigot part 1 and a socket part 2 of the concrete pipes connected by socket connection respectively, and a ring-shaped sealing member 4 is interposed between the circular angles 3 and 3′. Thereby, the socket part 2 takes charge of a concentrated load P such as soil pressure, and the ring-shaped sealing member 4 takes charge of watertightness. However, Cited Invention 1 fails to overcome the problem of the conventional concrete pipe, i.e. the breakdown of the socket part 2. Due to the breakdown of the socket part 2 and the twisting of the pipe, watertightness is easily broken.
Further, as shown in FIG. 3, Cited Invention 2 includes sewer pipes 210 and 210′, wherein the sewer pipe 210′ includes a socket part 211 that is provided with a slit 212, and a plurality of embedded nuts 222 that are provided adjacent to the slit 212, wherein the sewer pipe 210 includes a circular pipe part 213 that is provided with a fixing groove 214 in an outer circumference thereof, and wherein the sewer pipes 210 and 210′ include inner end steps 215 and 215′ that are formed in inner circumferences of the socket part 211 and the circular pipe part 213; an inner seal 230 having a circular ring 231 that is in close contact with the inner end steps and an insert part 232 that is integrally formed with the circular ring 231 and protrudes from the middle of an outer circumference of the circular ring 231 at a right angle; coupling rings 240 and 240′ that are inserted into the fixing groove 214 of the sewer pipe 210, are fixed to the socket part 211 of the other sewer pipe 210′, are coupled by nuts 248 and first bolts 246 passing through fastening holes 242 of coupling flanges 241, have external protection parts 244 formed outside slits 243 and making close contact with an outer surface of the socket part 211, are provided with fastening holes 242′ through which second bolts 246 pass and then are fastened to the embedded nuts 222, and are formed as a set in two; a packing 250 that is located inside the coupling rings 240 and 240′, has holes 251 through which the second bolts 246 pass in a horizontal direction, and are fixed in close contact with an end face of the socket part 211; and a bottom support 260 that is installed in close contact with the outer circumference of the circular pipe parts 213 of the sewer pipes 210 and 210′, has a rubber pad 267 attached to a round face of an arcuate body 261 thereof, is provided with anchor holes 262, through which anchors 270 pass, and connecting holes 263, into which connecting rods 275 are inserted, in vertical and horizontal directions respectively, so as to prevent arbitrary motion of the sewer pipes. With this construction, the problem of Cited Invention 1 is solved. However, Cited Invention 2 has disadvantages in that its connection construction is complicated, that many parts are used to inevitably increase the cost of production, and that a constructing process is complicated and requires much time.